Purpose:
The lipid analysis of human meibomian gland secretion (meibum) has been conducted by many research groups in an attempt to elucidate the pathogenesis of dry eye and meibomian gland dysfunction. However, due to difficulties associated with the collection of pure uncontaminated meibum and precise lipid analysis, the related data reported in previous studies have varied. The purpose of this present study was to reevaluate the methods of meibum collection and lipid analysis, and to more precisely elucidate the composition of fatty acids in human meibum.

Methods:
This study involved 4 healthy volunteer subjects (2 males and 2 females) ranging between 30 and 36 years of age. After a warm compression of the subjects’ eyes by use of a Panasonic electronic warm compression device (40°C, 10 minutes) on one day and without warm compression on another day, a spatula was used to obtain meibum from the eyes of each subject after a gentle squeezing of the eyelid margin by use of a meibomian gland compressor. Each meibum-sample collection was performed by use of a spatula that was thoroughly washed in high-grade organic solvents and then air-dried in order to avoid any possible lipid contamination. The obtained meibum was transmethylated, and then analyzed by use of gas chromatography-mass spectrometry (GC-MS).

Results:
The composition of fatty acids in the meibum samples was found to be similar between with and without warm compression, as well as between the male and female subjects. In the meibum samples, unsaturated fatty acids (monounsaturated: 52.0-56.5%; polyunsaturated: 3.6-3.9%) and branched fatty acids (34.7-37.6%) were found to be the major components, whereas saturated fatty acids (2.3-2.9%) were found to be only minor components. Moreover, those results were reproducibly obtained.

Conclusions:
The findings of this present study show that human meibum predominantly contains unsaturated- and branched fatty acids, which are different results from those reported in previous studies.